The present disclosure relates generally to x-ray tomography systems and, more specifically, to a tiltable gantry for x-ray tomography systems.
X-ray tomography systems have been used for many years to create images of cross-sectional slices of subjects, such as human patients, and are particularly used as a medical diagnostic aid. Computed tomography (xe2x80x9cCTxe2x80x9d) scan systems usually include an annular gantry including an outer ring secured to a stand and an inner ring mounted for rotation within the outer ring about a centrally located spin axis of the gantry.
The gantry is typically about six (6) feet in diameter and the inner ring carries x-ray tomography components, which can include an x-ray tube for providing the x-ray beam, an anode for acting as the focal spot for the x-ray beam, one or more high voltage power supplies, balancing weights, a data acquisition module, and a bank of detectors diametrically opposed from the x-ray source, or focal spot. Some of these components may be secured in the outer ring of the gantry; however, at least some are secured in the inner ring for rotation therewith.
A platform, such as a patient table, is positioned horizontally through the center of the annular gantry, generally in alignment with the centrally located spin axis of the gantry, so that a subject to be x-rayed or scanned is supported on the table between the x-ray source and the bank of detectors. The inner ring of the gantry then rotates about the subject during the scanning procedure and the gantry may be adapted to move axially with respect to the table during and/or between successive rotations of the inner ring.
Often it is desirable to precisely tilt the gantry about a tilt axis normal to the spin axis so that the spin axis of the gantry is made parallel to, as well as aligned with, the subject to be scanned. Such tilting of the gantry is done to set a scan plane of the x-ray tomography system. However, because of the relatively large size and heavy weight of the gantry and the x-ray tomography components supported therein, precisely tilting the gantry to set the scan plane can be difficult.
Some older mechanisms for tilting the gantry of an x-ray tomography system simply comprise a pivot arm linked to the gantry at the location of the pivotal mounting of the gantry to the stand. The gantry is tilted by applying torque to the pivot arm. However, because of the considerable size and mass of the gantry, tilting the gantry in such a manner requires significant torque. The significant torque requirement in turn requires a powerful expensive mechanism for applying the torque. Furthermore, the significant torque requirement can cause unstable motion (e.g., rocking) of the gantry during tilting.
U.S. Pat. No. Re. 36,415 to McKenna, entitled xe2x80x9cX-ray Tomography System with Gantry Pivot and Translation Controlxe2x80x9d, shows an improved, portable x-ray tomography system wherein tilting movement of the gantry is precisely controlled by mechanical displacement means which, in turn, are coupled to electro-mechanical means for monitoring the amount of tilting.
In particular, McKenna shows an annular gantry pivotally secured at arms extending radially outwardly from the gantry such that the gantry can tilt about the arms. A short member has an end fixed to one of the arms, and a ball nut is secured to the other end of the member. The member and the ball nut remain stationary while allowing an elongated screw element to move through the ball nut as a reversible motor rotates the screw element. The motor is mounted on an outer frame of the gantry, close to the pivot arm, and the screw element is suitably journaled in the outer frame so that the screw element freely rotates without moving longitudinally with respect to the outer frame. As the screw element rotates, therefore, the entire outer frame (and therefore the entire gantry) tilts about the arms. The screw element is also journaled in the outer frame so that the screw element can pivot about the motor as the gantry tilts.
An x-ray tomography system having a tilting gantry, wherein a relatively small force is required to tilt the gantry, would be an advancement in the art. Preferably, such a system will provide stable, accurate, and precisely controlled tilting of the gantry.
The present disclosure accordingly provides an apparatus that allows a gantry of an x-ray tomography device to be tilted with a minimum of applied force. The apparatus includes a tilt guide securable to one of the gantry and a stand of the x-ray tomography device, wherein the tilt guide is arcuate and has a center of curvature corresponding to a tilt axis of the gantry. The assembly also includes a drive mechanism securable to the other of the gantry and the stand. The drive mechanism has at least two spaced apart wheels, wherein each wheel operatively engages the tilt guide so that turning the wheels applies a substantially tangential force to the tilt guide to tilt the gantry about the tilt axis.
According to one aspect of the present disclosure, the apparatus includes a tilt lock movable against the tilt guide to hold the tilt guide in a fixed position. According to another aspect, the apparatus includes a tilt monitor providing a signal indicative of the amount of tilting. According to an additional aspect, the apparatus includes a tilt limiter for preventing further tilting upon reaching a predetermined maximum extent of tilt.
Other advantages of the presently disclosed frame with tiltable gantry, and apparatus and method for tilting a gantry, will become apparent by reference to the following detailed description taken in connection with the accompanying drawings.